4.1 – Apply Triangle Sum PropertiesA triangle is a polygon with three sides. A triangle with vertices A, B, and C is called “triangle ABC”.

4.1 – Apply Triangle Sum PropertiesExample 1:

Classify Triangle ABC by its sides and by its angles.

4.1 – Apply Triangle Sum PropertiesExample 2:

Draw an obtuse isosceles triangle and an acute scalene triangle.

4.1 – Apply Triangle Sum PropertiesWhen the sides of a polygon are extended,

other angles are formed. The original angles are the interior angles. The angles that form

linear pairs with the interior angles are the exterior angles.

4.1 – Apply Triangle Sum Properties

4.1 – Apply Triangle Sum Properties

Example 3: Find an angle measure.

Find m<JKM

4.1 – Apply Triangle Sum Properties

Example 4: Find an angle measure.

Find m<DEF

4.1 – Apply Triangle Sum Properties

A corollary to a theorem is a statement that can be proved easily using the theorem.

4.1 – Apply Triangle Sum Properties

Example 5:

The support for a skateboard ramp shown forms a right triangle. The measure of one acute angle in the triangle is five times the measure of the other. Find the measure of

each acute angle.